The present invention relates to a metal-resin composite having excellent corrosion resistance, and to a process of producing the metal-resin composite.
As employed in the specification and claims, the term "metal-resin composite" means a metal article, on one or more surfaces of which is present one or more adherent, cured resin layers.
In accordance with the present invention, the resin layer or layers on the surface of the metal article is of a nature such that the metal article exhibits excellent corrosion resistance, in particular, under acidic conditions.
There have been many investigations carried out for the purpose of imparting corrosion resistance to metal articles. Despite this, means for establishing excellent corrosion resistance for metal articles have not yet been achieved, at least as concerns present day corrosive conditions.
Zinc coated steel sheets have been widely used in building materials intended for outdoor exposure, for example, in erecting roofs, walls, etc. Tin plates have been widely used as materials for forming cans. Similarly, metals such as chromium, nickel, copper and aluminum have been widely used in the field of processed goods, such as foods.
Recently, however, the price of all of these metals has risen remarkably, due to a shortage of the metals. Further, stable supplies for some of the metals have been difficult.
Under these circumstances, there have been changes from using a heavy coating weight of metals, to using a low coating weight of metals. In the field of zinc coated steel sheets, electrogalvanized steel sheets have been widely used instead of galvanized steel sheets prepared by a hot-dip process. Similarly, in forming cans from tin plates, less tin is being used in coating steel sheets, and furthermore, the use of tin free steel, instead of tin plate, has increased remarkably, because of the rising price of tin.
The use of lower coating weights for the coating metals has increased the significance of chemically treating the metal to be coated. Many studies have been carried out involving chemical treatment to improve the corrosion resistance of a metal substrate having a low coating weight of metal coated thereon, but at present, the corrosion resistance of metal substrates having a low coating weight of metal coated thereon is still poor in comparison with metal substrates having a heavy coating weight of metal coated thereon.
Metal substrates coated with a paint have also been widely used when high corrosion resistance is required. In the case where the coating weight of the coating metal is low, the role of the paint film in providing corrosion resistance is of course an important one, and many studies concerning paint films have been carried out in recent years. For example, hard paint films have been employed in order to decrease the permeation of corrosive substances through the paint film. However, the extent of the corrosion resistance provided to the metal substrate by paint films is not yet sufficient, in view of the presently existing corrosive conditions.